Information and Advice Sexually Transmitted Infections Chlamydia Chlamydia Chlamydia is one of the most common STI’s in the UK and is easily passed on during sex. Most people don't experience any symptoms, so they are unaware they're infected.In women, chlamydia can cause pain or a burning sensation when urinating, a vaginal discharge, pain in the lower abdomen during or after sex, and bleeding during or after sex or between periods. It can also cause heavy periods. In men, chlamydia can cause pain or a burning sensation when urinating, a white, cloudy or watery discharge from the tip of the penis, and pain or tenderness in the testicles. It's also possible to have a chlamydia infection in your rectum, throat or eyes. If left untreated, chlamydia can lead to serious long-term health problems if left untreated, including infertility. Testing for chlamydia involves a urine test or by taking a swab of the affected area. Chlamydia is easily treated with antibiotics.